1. Field of the invention
The present invention relates to window stays and, more particularly, to friction window stays of the four bar linkage type.
2. Summary of the prior art
A four bar friction linkage window stay is described in U.S. Pat. No. 2,784,459 (Anderberg). This type of stay comprises a slider which is moveable along an elongate track which is fixed to the window frame. Two links each have one end pivotally mounted to the slider. The other end of one link is pivotally connected to a bar which is fixed to the frame of the openable window vent. A strut is pivotally mounted to the track and is also pivotally connected to the other end of the other link and to an intermediate point on the bar. In the closed position of the window the bar overlies the track with the links and strut inbetween the track and the bar. The end of the track is provided with a cap member into which the end of the bar seats in the closed position of the stay. Such window stays may be mounted to the window frame at each side of the window so that the window vent will pivot open about its top edge, or at the head and sill of the window so that the vent will pivot open about one of its side edges. The window vent is held in a desired open position by the friction between the slider and the track. The cap member provided at the end of the track typically comprises two relatively inclined, internal cam surfaces against the outer one of which an inclined edge of the end of the bar can close with a wedging action in order to bring the vent into its properly closed position. Ideally the end of the bar should be held relatively tightly in the cap member in the closed position of the vent so as to prevent forcing of the window or rattling in adverse weather conditions. However, it must still be possible to open the window in the normal way without excessive resistance being provided by the cap member. An example of a cap member using two such internal cam surfaces is described in No. GB-A-2 133 074.